Multi-channel devices have particular use in the field of chemical unit operations. For example, a plurality of channels can enable improved pressure containment and flow distribution when compared with a single channel capable of handling the same flow and can also provide greater surface area per unit volume. Examples of the most basic multi-channel devices include the well-known shell-and-tube heat exchanger and the plate-fin heat exchanger. In both exchangers, the flow of at least one fluid is distributed to a number of channels as it progresses through the unit. In the heat exchange environment, this increases heat transfer efficiency by increasing the surface area to which a given flowing fluid is exposed. Similarly, multi-channel configurations enable improved flow distribution and catalyst contact features in a reaction environment. It is also known that smaller and more compact devices can offer significant benefits such as improved thermal efficiency and faster reaction times. Most such devices have a smaller footprint with effectiveness measures comparable or superior to large-scale units. In addition, when employed as reactors, such devices often provide improved performance, both in terms of conversion of reactants to products and in terms of selectivity to desired products relative to undesired products. When employed as heat exchangers, such devices often provide improved heat transfer parameters.
Fabricating smaller and more compact multi-channel devices to meet economic constraints can be particularly difficult, especially when numerous small channels are required and the channels are in close proximity to one another. This is especially important when attempting to combine a multitude of small, compact devices to provide throughput comparable to large-scale units. Current fabrication methods for metals, for example, include, first, using wire electro-discharge machining (EDM) techniques to fabricate small multi-channel devices from solid blocks. In wire EDM, each channel is cut out by first forming a starter hole through the block. Then, each channel is cut to size by slowly moving the wire along what will become the walls of the channel. The material cut out is then scrap. While useful for forming relatively deep, narrow channels in solid material and minimizing assembly and alignment issues, wire EDM, compared to other techniques, is significantly more expensive. In addition, some practical limitations exist on channel lengths and fabrication time can be lengthy. Another method uses diffusion bonding of stacks of shims which have been stamped or cut out to define the multiple channels. In the first instance, stamping generates more waste material than other processes. Additionally, the diffusion bonding method requires that the channels be closed during bonding to avoid unsupported areas and then machined open after bonding. The bonding process itself also requires extensive tooling and expensive capital equipment. Following machining, cleaning steps are required to remove chips and cleaning coolant/lubricant. This all adds up to a process that is relatively expensive. Extrusion forms channels that require finish machining to reach desired levels of precision, thus adding to the cost. In addition, extrusion cannot be used on all materials—high temperature alloys, for example, are not good candidates—and there are limits on minimum channel size. Casting also suffers from some of the same limitations. Finally, etch techniques are not cost-competitive, particularly with high-temperature alloys.
A welded, or otherwise joined, stack approach as described herein represents a practical lower cost approach to fabricating such multi-channel devices.